Note: Descriptions are shown in the official language in which they were submitted.
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The present invention concerns an electric
accumulator cell with at least one dissoluble electrode,
containing a metal which on discharge forms a soluble
chemical compound. The cell further contains the remaining
components necessary for the functioning of aforesaid cell,
i.e., counter electrode, electrolyte and separators (or
spacers), etc. The invention concerns also such cells in
which the chemical compound formed during the discharge is
soluble by itself in the electrolyte used, but because
of special circumstances is immediately deposited as a
solid compound. Such circumstances may, for example, be
an over-saturated electrolyte or the addition of further
material with which the metal in question forms in the
electrolyte insoluble compounds. The invention is
applicable, e.g., for accumulator cells containing zinc
electrodes. These zinc electrodes form products soluble
in the electrolyte when discharged in an alkaline electro-
lyte. However, the electrolyte might be oversaturated and
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the zinc dissolved from the electrode during discharge,
will then be deposited from the electrolyte as solid zinc
oxide. The chemical reactlons during the discharge of
different electrodes in different electrolytes are not
fully known. In the example above and in the following,
certain intermediate products which might exist during the
chemical reactions for a short time are not taken into
consideration.
An important problem with cells with soluble
electrodes is obtaining a satisfactory life for the cell.
Cell life mainly depends upon the conditions pertaining to
the charging of discharged electrodes. During charging,
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the active material of the dissoluble electrodes shows a
tendency to form dendrites, growing out from the electrodes
in the direction of the counter electrodes, which dendrites
may thus easily cause short circuits. Furthermore, certain
effects at the edges, so-called shaping, may occur when
the active material is redeposited. Shaping causes the
layer of active material at the outer edges and lower
portions of the electrodes to show a tendency to increase
more in thickness than on the remainder of the electrode
surface.
Different methods have been tried to so:Lve these
problems, which have resulted in an increased life of the
cells, yet no fully satisfactory values were obtained. The
measures taken have, in many cases, led to more complicated
and thus more expensive cell constructions and were so
dependent on, for example, electrolyte concentrations and
other conditions within the cells, that the utility of the
cells became more circumscribed and the cost of the cells
has increased.
The present invention is also intended to solve
those problem8 and to produce a cell with a satisfactory
life by such methods of construction, which do not
circumscribe the utility of the cells, and make these cells
more appreciated from an economic point of view than
previously known cell constructions.
The construction of the dissoluble electrode is of
great importance in such a cell. Quite unexpectedly, it
has been proven that by building the electrodes according
to the invention from a body consisting of several layers,
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an electrode of exceptionally good reproduction qualities
can be obtained, while at the same time shaping tendencies
were substantially eliminated. By combining such a cell
construction with previously known methods to avoid the
formation of dendrites, a cell was obtained with
particularly good life expectancy.
It was known previously to build dissoluble
electrodes on a body of another material than the electro-
chemically active material. The use of such bodies which
are permeable to the electrolyte and have an enlarged
active surface is also previously known. The permeability
to the electrolyte is obtained either by using perforated
plates or by putting together the body from a fibrous
material, such as for example a net of metal threads. To
obtain a larger active surface of the body it has, for
example, been proposed when the body consisted of a sheet,
to pxess or emboss it to obtain a number of elevations
and depressions. Another method to obtain an uneven
surface is to use a sheet of varying thickness at different
points of its surface. If the body is formed from fibers,
these fibers can either be oriented in a pattern as, for
example, in a woven net or unoriented as in a mat of the
non woven type. The body of the last mentionecl type can
be prefabricated, more thick than finally required, where-
after the bodies are mechanically compressed. Thus the
mechanical strength of the body is increased while a large
active surface is maintained.
The most used method to avoid the harmful effects
of dendrite formation is to surround the dissolving
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electrode by a separator which is so dense that the dendrites
are unable to penetrate through the separator. The use of
such dense separators is naturally accompanied by a limita-
tion of electrochemical properties of the cell and thus of
its utility. It has been shown that the life of such separ-
ators is insufficient for the demands put on the life of
the cell.
Another method to limit the growth of dendrite is
to supply the cell with a scraper or similar device, which
moves along the surface of the electrode and scrapes away
the protruding dendrites. Instead of scrapers, rollers may
be used and they can be made in such a way that protruding
dendrites are not scraped away from the electrodes, but onl-
pressed back into the electrode again whereby they can con-
tinue to work as active material. It is even possible to
use non-moving scrapers or other mechanical devices against
moving electrodes. However, not even by these means it
was possible to fulfill the demands put on the cells. Fin-
ally it has been proposed to vibrate the dissoluble elec-
trodes and/or the separators or spacers. By the turbulancewhich thus occurs in the electrolyte, nearest to the elec-
trode surface, an effect was achieved which inhibits the
formation of dendrites.
A cell according to the invention has a dissoluble
electrode, which is built upon a body which is insoluble in
; the electrolyte, mainly consisting of inert material, com-
prising at least one centrally located conducting layer on
each side of which there is an outer layer, each layer being
composed of an inert conducting material insoluble in the
electrolyte.
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The planar sides of the outer layers are smaller than the planar
sides of the central layer so that the central layer has a
bare portion about its periphery. A part of this bare portion
is covered with an electrically insulating material, the width
of the uncovered bare portion between the insulating material
and the outer layer being at least twice the thickness of the
outer layer.
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Preferentially all these layers are perforated or porous in
some way. By inert is meant that the body does not consist
of a material participating in the electro-chemical reactions
of the cell. The central part may suitably consist of a
perforated metal sheet or a fabric of metal threads. It
may even consist of a non conducting material with a
conducting outer layer e.g., plastic with a metal coating.
The present invention requires not only the central body
but also at least one more layer on each side of the
central body, which shall be a separate layer not
directly connected with the entire surface of the central
layer. The outer layer may be formed of the same or
different material than the central layer. The outer layer
preferably is formed of a net of metal or of metal coated
plastic but may even be formed from a plastic netting with-
out further coating which, however, presupposes that the
active material of the electrode has sufficient electrical
conductivity by itself. The outer layers are suitably
connected to each other by welding, brazing or other methods
with the connections made at points and going through the
openings in the central layer. Direct mechanical connection
; between the outer layers and the central layer should be
avoided or at least be restricted to a number of points at
only one edge (mainly because it becomes difficult to
obtain fully plane bodies during their production).
It has been shown with cells according to the
invention that the shaping effect will be eliminated in a
surprisingly simple fashion when the outer layer has a
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slightly lesser extension along the plane surface of the
central layer and thus leaves the edges of the central
layer bare. Furthermore, the fact that a part of the outer
bare edges is covered by an insulating material makes the
conducting surface of the dissoluble electrode somewhat
smaller than that of the counter electrode. By "surface"
is understood the geometrically projected dimension regar-
dless of the size of the electrochemically active surface,
which as previously mentioned may be influenced by corruga-
ting, perforating or by other means.
-~ It has been shown that very suitable working con-
ditions are obtained for the cell, if in a cell according
to the invention the dissoluble electrode or the surrounding
separators of spacers are so installed that they vibrate in
a direction parallel to the plane surface of the electrode.
The zinc anode and/or separator is vibrated in the direc-
tion of the plane of the anode or separator at a frequency
and amplitude during the charging process sufficient to
inhibit dendrite growth on the zinc anode. The vibra-
ting part is mounted so that all portions thereof move
substantially the same distance during each cycle of vibra-
tion and all portions of the vibrating part move in a
reciprocating manner to have at the same moment the same
rectilinear movement during all portions of the vibration
cycle. The vibrating part may be vibrated at a frequency
of from about 0.1 to 500 Hz and an amplitude sufficient to
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inhibit dendrite growth amplitude generally will be in the
range of from about 1 to about 10 mm. or more. As the
frequency of the vibration may be relatively high, the
vibrating components may be placed in vertical guiding
tracks. Suitably, all the electrodes are placed in such
guiding tracks. Preferably, the insulating material on
the edge of the central layer extends outside the guiding
tracks, so that the surface of the dissoluble electrode
remains smaller than that of the counter electrode. Under
these conditions, very good reproduction qualities are
obtained for the charging and discharging cycles and a
long life of the cells is also obtained. This is
especially true if the body is dimensioned in such a way
that the active material of the dissoluble electrode does
not fully fill up the holes in the outer layer, when the
cell is fully charged.
The invention shall hereinafter be more closely
described with reference to the accompanying drawings. At
the same time the favorable effects which unexpectedly
have been attained by the invention will be explained to
a certain extent. Furthermore, a preferred embodiment of
the invention, which is utilized in connection with zinc
electrodes will be described as it is expected that the
invention has special utility in cells with such electrodes.
Figure 1 shows a cross section of a cell in
accordance with the invention. Figure 2 shows a dissoluble
electrode to be used in such a cell and Figure 3 shows a
cross section of such an electrode. Figure 4 is a partial
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view of electrodes in a cell in accordance with the
invention and a part of a plate with guiding tracks.
In Figure 1, a cross section of the cell at right
angle to the electrodes is shown. The cell contains a
number of dissoluble electrodes 1 and counter electrodes 2.
Between these are situated the separators or spacers 3.
The dissoluble electrodes are connected by connecting
devices 4 to a common bridge 5. The dissoluble electrodes
are arranged to be vibrated by a shaft 6, which is
journaled between bearings 8 in the cell wall 12. The
shaft is eccentrically formed and the vibratory movement is
imparted by shaft 6 by suitable means outside the cell (not
shown) and is imparted to electrodes through the yoke 7 and
suspension and connecting devices 18 and 19. The shaft 6
is electrically insulated from the electrodes, e.g., by
using connecting devices made of an insulating material.
Through a flexible cord 17 the electrodes are connected
to a pole post 11 on the outside. The electrodes 2 may
similarly be connected to post 11 by conventional means,
not shown.
The electrode shown in Figures 2 and 3 has a body
built upon a central layer 13 which may consist of a plate
with perforations 21. On each side of central layer 13 is
disposed an outer layer 14 and 14' whi~h may also consist
of a porous or perforated net. These two nets 14 and 14'
may be made from metal or plastic or metal coated plastic
and are attached to each other by welding or cementing.
The attachments are made at points through the perforations
21 of the sheet 13. In that manner, the three layers, 13,
14 and 14' of the electrode body act together as one unit
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without a direct mechanical connection between the outer
layers 14 and 14' and the central layer 13. The central
layer 13 is provided with an electrically insulating
material 15, which may be a U-shaped profile from a
suitable plastic material or a layer of insulatlng lacquer
around the outer edges. The size of the outer layer 14
and 14' are so much smaller than that of the central layer
13 that a bare edge 16 is formed on the sheet. The width
of the bare edge 6 should be at least double that of the
thickness of the outer layer 14 or 14'.
Figure 4 shows a number of dissoluble electrodes
la and counter electrodes 2 of which one vertical side is
placed in a guiding track 32 in a disc 31. For a better
lucidity only parts of the electrodes are shown. A
complete cell has two discs with guiding tracks one on
each side of the group of electrodes. The guiding tracks
32 may even be an integral part of the cell wall. From
the Figure it can be seen that the insulating layer at the
outer edge of the dissoluble electrode is covering so
much of the electrode that this layer covers a small part
of the electrode outside the guiding track. Thereby it is
achieved that the dissoluble electrode has a smaller and
le~s wide electrochemically active surface than the
counter electrode. As shown in the art, this may also be
achieved by a special configuration of the disc.
The invention is additionally illustrated in
connection with the following Examples which are to be
considered as illustrative of the present invention. It
should be understood, however, that the invention is not
limited to the specific details of the Examples.
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ExAMæLE 1
An electrode according to the invention was produced
starting from a perforated iron sheet 13. The sheet was
0.5 mm thick, with a length of 200 mm and width of 140 mm.
The sheet was perforated with circular holes 21, diameter
about 6 mm, covering about 50% of the surface. On each side
of the plate was disposed a net made of nickel plated iron,
thickness of threads 0.5 mm, with the threads being 2 mm
apart from each other. The nets 14 and 14' were 185 mm
long and 125 wide and were placed centrally on each side of
the iron sheet. Thereby a bare edge of 7.5 mm width was
obtained at the circumference of the sheet. The nets were
attached to each other by pressure welding them together
through some of the perforations 21. The number of welding
points was 20. Having attached connecting device 4 to the
body, the outer edges of the sheet were insulated to a
width of 5 mm on both sides applying an insulating lacquer
15. The meshes of the nets were 50% filled by zinc oxide
conventionally used for zinc electrode6. Thereafter the
electrodes are together with the counter electrodes placed
in the container. The counter electrodes are nickel
electrodes of the conventional type. Between the
electrodes, 6eparators are interfoliated and along ~he
length of the guiding tracks are adjusted in such a way that
they cover the outer edges of the electrodes to the dashed
` line 22 as ~hown in Figure 2. The electrolyte in the cell
was a conventional solution of potassium hydroxide in water
~ with the usual additives.
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EXAMPLE 2
The electrodes were produced as describe~ above in
Example 1, but no active material was applied. The body was
placed in a cell container together with counter electrodes
and arranged for vibrations at a frequency of 50 Hz and an
amplitude of 4 mm. The electrolyte in the cell was 6 molar
potassium hydroxide, containing 100 g zinc oxide per liter.
The thus obtained cell was charged with a 15 A current and
a deposition of zinc was observed on the electrode body.
In the beginning of charging, a zinc deposit was formed only
on the sheet 13 inside the meshes of the nets 14 and 14'.
Some deposition occured even at the bare edges 16 outside
the nets. On the r.ets 14 and 14' a certain amount of
hydrogen gassing was observed, but no deposition of zinc.
After about 15 minutes of charging a deposition of zinc
also occured on the nets 14 and 14'. This deposition was,
however, very thin at the outside of the netting and
absolutely free of dendrites. Also along the edges 16 of
central layer 13 further deposition of zinc occured,
through its amount was not larger than the deposition on
the nets 14 and 14' and no protruding dendrites were formed
on the edges 16.
E~AMPLE 3
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A cell was built as described above in Example 2,
but having 4 dissoluble electrodes and nickel oxide counter
electrodes of the conventional type. The counter electrodes
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were dimensioned in such a way that the active material was
deposited on the soluble electrodes in such an amount that
the space within the meshes of the nets 14 and 14' was
filled to 50% with zinc when obtaining the corresponding
capacity. Such a cell was undergoing cycling, i.e.,
repeated charges and discharges, according to a pre-
determined scheme. With each such cycle, there occurs a
full or part dissolution of the newly formed active layer
of the dissoluble electrode. A~ter 800 cycles, cells
made according to the invention showed still mainly un-
changed properties.
As shown by aforementioned Examples, the cells
prepared in accordance with the invention had a surprisingly
improved life. That is caused by the fact that the
formation of dendrites and so called shaping at the edges
of the electrodes has been avoided.
` The principles, preferred embodiments and modes of
operation of the present invention have been described in
the foregoing specification. The invention which is
intended to be protected herein, however, is not to be
construed as limited to the particular forms dlscl~sed,
since the~e are to be regarded as illustratlve rather than
restrictive. Variations and changes may be made by those
skilled in the art without departing from the ~3pixit of the
invention.
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